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This, shockingly enough, isn’t about espresso. It is about brewed coffee, and the fact that brew temperature is completely wrecking my head. We talk a lot about brew temperature but what we are really talking about is water delivery temperature.

I love my Uber boiler, I love the control and the delivery temp stability. With this, however, has come the painful and embarrassing realisation that it doesn’t matter. Alright, that is perhaps an overstatement – temperature has massive influence on the quality of the brew, that is undeniable. I may love the control of the Uber, but having a consistent and controllable temperature really just shifts the problem from the exit spout to the vessel underneath.

Espresso has a rare advantage as, despite being the most finicky and frustrating brewing method, when it comes to brew temperature we can be pretty sure it is close to the delivery temperature. We’ve enclosed the brewing space and have a lot more consistency that way. Put a Scace device in and measure and the number you get is as close as we can measure what the coffee would be subjected to during the brewing. With a french press this is all very different.

Once you open up the brew environment a lot more factors suddenly influence the brew temperature. The distance from exit to vessel, the temperature of the press itself, the material of the press, the level of insulation, the size of the press and the ambient temperature will all influence the brew temperature: the temperature of the coffee and water as they steep/brew.

In the filter brewing sector/literature we generally see a prescribed brew temperature of 92-96c measured at spray head. We don’t see much on actual brewing liquid temperature. Surely a plastic brew basket will create a hotter brew than a metal pan? Will a recently used hot pan brew hotter than the first brew of the day – despite stable water delivery temperatures? Is there any research on this?

I’d like to create a few experiments with the Extract Mojo looking at the effect on brew temperature across the brew (though I’d appreciate any help from other people out there?). Does starting temperature matter more than total temperature spent? If my brewing vessel radiates heat quicker – because it is wider – can I match a better insulated brew by starting hotter?

I have a few simple experiments in mind that I shall try and perform and post about during the week. In the mean time any and all thoughts are welcome!

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23 Comments

This is exactly the reason I’ve been so impressed with vacpots. It’s the technique with the best temperature control. There’s a reason that organic chemistry labs use the exact same setup (but they call it a reflux machine, but that’s organic chemists for you.)

My understanding from talking to Mr Stack was that one of the standards referred to 94 C (ish) in the bed, as opposed to the more common at the head (possibly the Norwegians…?).

I’m with you on the plastic front. Plastic is a poor conductor of heat, so it pulls less heat out of the liquid (and also radiates less heat out of the system). While I quite like preheating the Bodum Columbia and using that, I can’t help but think that a super thin glass double walled press would be better.

Like those Bodum Pavina glasses that cause everyone to burn their mouths when used with coffee…

On the retailing side, I’ve brewed coffees side by side- comparing preheated vs. room temp vessels. Most recently I compared a warmed up Hario v60 vs. a cool one. The filter paper was prewet in both instances, and everything else was the same- water temp, pouring style, etc. When I was finished brewing the coffees I let them cool a bit, and tasted them side by side. Initially I didn’t notice much of a difference, but as the cups cooled the preheated v60 had a much more pleasing finish to it, while the “cold” one was noticeably less desirable. To make sure I wasn’t prejudiced I let my baristas taste it blind- they liked the preheated guy better.
This is something I’ve always done out of habit, akin to leaving the portafilter in the group head to prevent the cold metal from drawing down the water temp delivered to the coffee. But it wasn’t until I tried them side by side that I was absolutely certain this was a necessary step.
My next questions are… if you use hotter water on a cooler brewer, do you need to preheat the brewer at all and does the hotter water adversely effect the coffee? My guess is that it could give the coffee a burned taste, but it would be interesting to try.

James – congratulations on the post,
To clarify David’s point:
SCAE Gold Cup says the temperature should be:
– 92°C to 96°C as water is emerging out of spray head
– Throughout 90 to 100% of brew cycle

Norwegian Coffee Association say the temperature should :
– be read in the coffee bed by placing the thermocouple on top of the bed.
– reach 92°C within 10% of the total brew time.
– never drop below nor climb above 92°C to 96°C thereafter in the bed.

I believe 96°C in the bed is too hot for what it’s worth.

Regarding temp stability, on small baskets/brew volumes, metal baskets result in less stable temperatures in the bed.

Andrew Lopez and I have been kicking this idea around for the last few months. Brew temp is just another variable, that can be manipulated not only at the beginning of a brew but throughout the whole process, much like pressure profiling.

Have you ever noticed that there is something different and unique about a really good cold brewed coffee? Qualities you don’t get in regular brewed coffee, but you do get out of a 16hr cold brew.

Brewing coffee at the temperatures we do (195f-205f) seems to be the best option if your looking to brew coffee in the 3-5 minute range, but what if I don’t need coffee that fast what if I want to brew coffee at 175F and brew it for 8 minutes? Couldn’t that yield that same parameters Gold Cup parameters but in a different way? And couldn’t it yield a completely different TASTING cup?

And isn’t it obvious a 16hr cold brew yields less acidity but more caffeine? What exactly are we extracting, and do certain things get more or less extracted based on how high or low the temperature is, or maybe something doesn’t get extracted at all?

Can we create profiles of temp? We have played around a little with brewing presses and changing temp throughout brew, but we would love to do more experiments with a Extract Mojo (HINT HINT. SOMEONE READING THIS SEND ME ONE!!) and the UberBoiler…let us know what you find or if we can help in any way?

Ps. Does the UberBoiler offer change in delivery temp instantaneously or just one temp consistently?

I remember discussing a similar thing some years ago (I think it was on coffeed) wether to pre heat cupping cups or not. There is clearly a difference in brew water temperature and taste, but I wonder why we did not take it further?? Maybe we were just too hung up on espresso machine water temperatures?? Or just too damn lazy… I think Clover adressed this by having a heating element around the brew chamber that allows you to control the temperature of the brew chamber. I experimented with it when I got the clover and the best results came with higher temperatures, as the water temperature drops rapidly while brewing on the Clover. Maybe the next trend in coffee will be heating blankets to wrap around our brewing equipment :-)

I remember you posting about the cups, and the effect it had. It has been interesting to add a very stable water temp source into cupping, because it exposes the flaws in kettles and the inconsistency it brings. Add cups coming from the cupboard or the glass washer and your brew temp goes all over the place.

I charted out a very quick hot press vs cold press (using a bodum dual walled press) and the colder one sat pretty much 3C below the preheated one. After s 5 minute steep the difference in extraction was about 0.5% – though I’d need to do a lot more of these to have any useful or statistically significant results (with the hotter obviously extracting more).

I totally agree that there is too much inconsistensies around in a lot of cupping sessions. Although I am quite happy with my water boiler and the stability it has given in temperatures during smaller cupping sessions, I have yet to test it with my newly arrived Extractmojo. I can’t wait to start working with it, dismissing my old brixmeter and “tds- bingo- meter”

I am actually getting more and more keen on getting an Über boiler and maybe replacing the good old Clover… maybe next year…

The lack of a system to link brewing parameters to sensory analysis and the individual effect each parameter has on different aspects of the analysis would be too long a thread. So I posted this ‘Mixing Desk’ concept last night ‘cos it was burning my head. http://marco.ie/uberproject/?p=226. Does anyhting else exist to link the science to the sensory?

Being primarily an Aeropress user, I have inadvertently, in the past, brewed coffee at 175 (or less) by accident and found that, depending on the roast, the results weren’t necessarily bad. In fact, one morning, I was so sleepy that I actually forgot to heat the water! About halfway into the process, I realized what I’d done and just went with it. The resulting cup was surprisingly good! Maybe not as complex, but still very drinkable.

As for French presses, I have come to love the Bodum Columbia for its insulating properties. If I put a digital thermometer in the top while I’m steeping, it barely moves the whole time, and that’s with the lid off. I suspect that the amount of grounds one uses would affect this as they would tend to trap more heat inside?

Is it possible that brew times and temps are linked to each other? eg. cold brewing takes 6-8 hours in the fridge with water having a temp of 2-10 c°. To brewing only 3-4 mins @ 92c° So it is possible that brewing colder takes a longer time but can extract as much flavor? I have experimented with cold brewing green tea (sencha and gyukuro) as it doesn’t take heat very well 60c° is about the max. cold brewing the green tea produced better results imho.

Now this would be interesting to research. eg. I would like to know the brew time for coffee @ 30c°. Think of the new flavor profiles, machines, roast profiles. Imagine a special bean or roast for a 2 hour brew @ body temperature, no need for boiling water!

That different coffees will react well to some temps more than others is something we are used to. But there is a need to describe brew temps better than by the output temp, maybe a average temp at the start of brewing in the brew vessel. This would be less useful in espresso but more so in press or other types of brewing.

you are saying that output temperature from lets say a boiling water from a kettle to pouring that water on the ground coffee resulting in the brewing muck should be researched and clarified. This implies knowing the humidity, ambient temperature and temperature of the brewing device itself.

Jeff: time and temperature are linked in a complicated way, and would be differently so for different substances. Hence, the change in rates of extraction for various compounds with temperature will not be the same.

Consequence: coffee extracted at low temperature for longer time will inevitably have a different flavour than coffee extracted for a shorter time at a higher temperature.

A simple model experiment is to make tea and compare degree of astringency and bitterness. Steep the leaves in water at ambient temperature for as long as you like and see if you can make a tea that tastes as astringent and/or bitter as one that is overextracted for just a few minutes at high temperature.

For scientific studies on coffee extraction, look for references to Michael Spiro which has published loads on the topic for more than two decades.

I’ve often wondered if the people who say they prefer to french press their coffees, as opposed to brewing them in a vacpot, prefer it because of the lower temp the french press tends to brew at. If I start with a room temp french press (10 oz, glass) it brews around 185 F. I tried to see what the lowest I could get my vacpot to so I could compare the cups together, and could only get it to 192 F. I still want to try some other things to lower this temperture but this is certainly something to think about.

Erik, thank you for referring to that author. I have looked into him, and will read his work. Brewing longer at lower temperatures definitely changes the taste, but the amount of flavor seems comparable to classic methods. I think that some flavors can only be extracted if the brew is exposed to higher temperatures, but also, I think that deeper, earthier flavors can only come to their right if extracted at lower temperatures and longer times. The heat could have an adverse effect to that range of flavors.

James, just a quick note on the vessel: I usually preheat the brewing wessel with boiling water, then measure the temperature of that water before tossing it out. This to try to be as consistent as possible with vessel temperature before brewing. For french press I use a pre-heat temp of 80 degrees celsius, more because it’s easy replicable than anything else. Thoughts?

just got my datalogger and made a few tests with it. It all really depends how you brew your coffee, is it with a boiler that can supply water at a steady temperature throughout the whole process, with slow flow and good dispersion, or is it using a kettle and pouring from it manually? I normally use an ordinary kettle to boil the water (not PIDed yet), transfer that to a metal jug, let it cool to around 92*C and pour. Today I measured the temperature under the coffee bed and it’s 85*C at the beginning and 82*C at the end, the coffee itself was 72*C. I know that it’s only one test, but I was curious if anyone did anything similar and what differences did he/she find.

I’ve been thinking about this for tea for some time, and of course, it’s equally valid for coffee. I started brewing tea at home inside a simmering pan of water. I figure it’s about as controlled as I can get with the simplest of hardware.

I’ve been exploring this topic lately b/c admittingly I’m curious just how serious managing heat w/ brewing water temp is. Surely I need a better thermometer (or do i?) but the studies I’ve been conducting have been 3 basic profiles water temp, 1-just off boil / 93c in the bed… 2-preheated kettle/brewer / 90-91c in the bed….. and intentionally cool / 85c in the kettle then 79-80c in the bed. Not surprising, results were somewhat linear, correlating hotter temps with higher extractions, but what I thought odd was that extraction %’s weren’t as drastically different as I thought they’d be. I was even able to produce a 19% extraction with the coolest temps… they didn’t taste great, but may seem ok if you’re only paying attention to ext% (which is why that’s not all one can value.)

From digging around I feel the main and maybe only principal on this topic is the correlation between sensory perception and temperature. Yes, there is a correlation between extraction% but from what I’ve done I’ve found those numbers aren’t solely able to signify quality.

Even in Scott Rao’s book ‘everything but espresso’ temperature is only one paragraph and with that citations from Ted Lingle’s brewing handbook as well as ‘experiments conducted by the author.’

With all this I can’t help but wonder if managing temps is really worth the external investments of hot-plates and other additional techniques that someone might incorporate into their brewing routine.